Over the surface of the earth there are many thousands of oil wells that are drilled and completed in unconsolidated sand, i.e. crumbly sandstone. In such wells, sand does not necessarily precipitate to the bottom of the well, but instead may remain in suspension and is pumped up, if not free flowing, with the oil. As a result, most mechanical parts as valves, bearings, pistons, cylinders, etc. wear out prematurely under such conditions. Accordingly, the sand must be filtered out from the oil, preferably in the well. Petroleum companies have spent large sums of money in trying to find a suitable solution to the sand problem, but heretofore there has been no satisfactory method or long lasting device for preventing the entry of sand into the tube string and eventually into the suction pipe of the pump, or other works.
U.S. Pat. No. 2,837,032 discloses an oil well foam and wire coil filter, but that filter is quite sophisticated and expensive to manufacture, and is not adjustable to be opened for backwashing a cleaning liquid, as water, to clean the clogged filter. Another attempted solution was a spring filter as disclosed in U.S. Pat. No. 3,754,651, but because no spacers are apparent between the helical filter elements, the elements would have to be held in slight tension to separate the helical filter elements during filtering. Thus that filter could not be used as an oil well filter on which high compressive loads may be placed. Likewise no guide tube or mandrel can be utilized to strengthen the compressive capabilities for converting the filter to one for use in wells. Also, the spring filter of U.S. Pat. No. 3,179,116 is capable of being strengthened to use in wells. Any compressive force on the triangular spring elements would cause them to collapse, and further the coined depressions for separating the spring elements would cause the spring elements to flex with a load thereon causing displacement of the adjacent coils and variation of the gauge therebetween.
Thus, new and better methods for filtering sand from an oil well, better methods for forming and assembling helical spring sand filters, and better self-cleaning helical spring sand filters are required for mounting on the lower end of a tubing string extending down into a well to the oil containing sand strata.
The disclosed inventions are improvements over those of Assignee's U.S. Pat. Nos. 3,901,320 (166-311) and 3,937,281 (166-233).